The ability to sense changes in properties within narrow regions, such as narrow body lumens, is of increasing interest for research and diagnostic or analytical purposes. For example, the human heart pumps blood through the body and the measurement of blood pressure within blood vessels is of interest for characterising a circulatory system of a patient. Another example relates to diagnostic needs to measure a distribution of pressures exerted by muscles around the alimentary canal, which moves food from the mouth into the stomach. Further, there are many examples in other fields of technology that require measurements of properties in narrow areas, such as in water or gas pipes.
Optical devices for monitoring such properties are now being developed. The optical devices may comprise an optical fibre Bragg grating, which has an optical response that depends on a strain of the Bragg grating. The strain on the Bragg grating can be applied by a “squeezing” force in the vicinity of the Bragg grating and the resultant change in strain shifts a wavelength of an optical response to a different wavelength range. Such optical properties have the advantage that they are usually smaller than electrical or mechanical devices for measuring the change in the property. Further, an optical fibre may include a number of such Bragg gratings and each grating may be arranged to give a different optical response (for example at a different wavelength range). Consequently, it is possible to analyse a distribution of pressures.
However, such optical systems still have significant drawbacks. For example, it is often not possible, or it is inconvenient and unreliable to correct a measurement of a change in a property, such as a pressure, for differential temperature change especially if a probe of the optical system has to be very narrow.